The natural anatomical joint structures of an individual may undergo degenerative changes due to a variety of reasons, including injury, osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis. When such damage or degenerative changes become far advanced and/or irreversible, it may ultimately become necessary to replace all or a portion of the native joint structures with prosthetic joint components. Joint replacement is a well-tolerated surgical procedure that can help relieve pain and restore function in injured and/or severely diseased joints, and a wide variety of prosthetic joints are well known in the art, with different types and shapes of joint replacement components commercially available to treat a wide variety of joint conditions.
Historically, joint implant components were provided in a limited number of sizes and/or shapes, typically allowing for a one-size-fits-all or few-sizes-fit-all approach (i.e., multi-component and/or modular systems). More recently, the surgical community has come to embrace the concept of “patient-specific” and/or “patient-adapted” joint implant components (and associated surgical tools and procedural steps), in which one or more joint implant components is particularized in various manners for an individual patient. These newer techniques and implants typically utilize pre-operative anatomical image data of the patient (as well as computerized modeling and/or manipulation of such data, etc.), which is utilized to select and/or design appropriate features of an implant component that accommodate relevant features of the patient's actual anatomy. Such systems can include the selection of pre-manufactured implants or “blanks” to be modified in some manner (to accommodate various anatomical needs and/or limitations of the patient) as well as allowing for the design and manufacture of a unique implant that matches some or all of the patient's individual anatomy.
Regardless of the type of implant components utilized, there comes a point during every joint replacement/resurfacing procedure where the surgeon will desirably test or “balance” the joint, typically evaluating the tension and/or laxity of surrounding soft tissues and/or ligaments, as well as checking for proper motion and/or operation of the joint with the implant components (or possibly “trial components”) implanted into the patient. Proper balancing of soft tissue and ligament tension/laxity is important during such procedures as a surgical repair resulting in excessive laxity can lead to an unstable joint, while excessive soft tissue and ligament tension can limit functionality of the joint replacement as well as lead to significant patient pain. Moreover, a joint replacement having poor kinematics can similarly significantly impact joint function and cause patient pain, as well as affect implant long term durability and/or performance.
In many surgical procedures, a portion of the procedure for balancing a joint (and associated implant components) is accomplished by introducing a series of inserts or spacers into an articulating surface (or other location) between bones and/or implant components of a joint, with each spacer having a differing thickness and/or shape to distract the relevant adjacent structures. Once an individual spacer is introduced, the surgeon can then assess the tension and/or laxity of the relevant soft tissue structures, and decide whether the current spacer creates a desired spacing of the joint, or whether a different size/shape of spacer is desirous. The surgeon can remove and replace the spacer as desired (choosing differing thicknesses and/or shapes), until a desired spacing and/or alignment of the various bones, implants, trials and/or other joint structures/components has been obtained. The surgeon can then desirably utilize information regarding the size and/or shape of the relevant chosen spacer(s) to verify and/or modify desired joint function in a variety of known manners. For joints having multiple articulations, multiple spacers for each articulation can be employed. In at least one example, the use of such spacers during a surgical procedure can guide the surgeon in choosing a desirable thickness of a polyethylene insert for insertion into a tibial tray of a knee implant component.
Implant balancing techniques are generally required during the implantation of a one-size-fits-all or few-sizes-fit-all approach, but even where a custom device, tools and/or the surgical procedure have been created or selected using patient-specific image data for an individual patient, it is often still desirable to conduct a balancing and assessment procedure on the relevant joint structures during the patient-specific and/or patient-adapted implantation procedure. Because access to the relevant joint structures typically involves cutting and/or distraction of various soft tissues surrounding the joint, as well as preparation of various anatomical support structures, the forces and relationships between the various tissue structures can be significantly altered by such surgical acts during the surgical procedure, which can have significant consequences on the kinematics of the knee that were unanticipated prior to the actual procedure. Moreover, because the joint is typically in a significantly damaged or diseased condition (thus necessitating the surgical intervention), and soft tissues including cartilage and/or ligaments can be difficult to visualize and/or differentiate, it may not be possible to precisely determine the kinematics and/or balancing of the knee solely from image data obtained prior to implantation of the implant components and/or trials. In addition, the use of balancing and measuring techniques can inform the surgeon of unanticipated complications (i.e., an incorrect surgical cut has been performed and/or an implant size and/or shape is incorrect), which can allow the surgeon an opportunity to modify the surgical procedure in some manner in an attempt to produce acceptable results.
Currently, measurement and/or assessment systems do not readily and conveniently facilitate a surgeon's balancing of the joint and/or joint implant components during the surgical procedure. Current inserts, spacers and/or other measurement tools utilized during joint balancing procedures typically involve a significant number of individual tools of differing sizes and/or shapes, with each spacer constituting a separate surgical instrument. Aside from occupying a significant amount of “real estate” in the sterile field, the use of multiple measuring tools of this type generally require multiple tool exchanges between the surgeon and back-table personnel, which can increase the opportunity for dropped tools, loss of sterility and/or interfere with the surgeon's concentration during the procedure. These difficulties can be further exacerbated as the surgeon attempts to manipulate the joint and/or release various soft tissue attachment points, as the surgeon will subsequently desire to measure and/or verify the changed balance of the joint, again mandating additional tool exchanges. In many cases, the multiple options presented by such tools and tool exchanges can be confusing for many surgeons, especially in situations where obvious visual landmarks may no longer be present (such as during revision procedures), making alignment and restoration of the joint line even more difficult.